Dual X-ray absorptiometry (DXA) has a range of clinical applications, from assessing associations between adipose or lean body mass and the risk of disease to measuring the effects of dietary interventions on adipose deposition and oxidation and/or muscle accumulation. Many lifestyle-related studies, however, are short- to medium-term interventions, and inter- or intradevice variation between DXA scanners can facilitate type I and type II errors during data analysis. Studies demonstrate that variation in body composition measurements exist not only between DXA instruments using fan-beam and pencil-beam technologies but also between DXA instruments produced by different manufacturers. Moreover, studies show inter- and intrainstrument variation between identical DXA instruments. Such inter- and intrascan variability between instruments can be compounded by the particular patient population being investigated. The objective of this review is to discuss inter- and intradevice variation of DXA instruments and to outline quality control procedures that should be implemented prior to initiating short-term single or multicenter clinical trials that use DXA to investigate the effects of an intervention on loss or accretion of lean or fat mass.